Amplifier with negative voltage feed-back



Oct. 23, 1956 P. J. H. JANSSEN 3,768,325

AMPLIFIER WITH NEGATIVE VOLTAGE FEED-BACK Fil ed Feb. 9, 1953 IN VEN TOR PETE R JOHANN ES HUBERTUS JAN SSEN AGENT AMPLIFIER WITH NEGATIVE VOLTAGE FEED-BACK Hubertus Jansseu, Netherlands, assignor to and Trust Company,

Peter Johannes Emmasingel, Eind- Application February 9, 1953, Serial No. 335,845

Claims priority, application Netherlands February 21, 1952 Claims. (Cl. 315-27) The invention relates to an amplifier having negative voltage feed-back and an output impedance, the value of which varies owing to temperature fluctuations.

Amplifiers of this kind are often used, inter alia, for the supply of the deflection current for a deflection coil of a cathode-ray tube, negative voltage feed-back being carried out in the amplifier, for example, for linearising the deflection current.

When using such an amplifier, for example, in a television receiver, the temperature of the deflection coil increases after the receiver has been switched on.

The negative feed-back voltage tends to keep the output voltage of the amplifier constant. However, since the resistance of the deflection coil, increases owing to the rise in temperature, the current passing through this coil will decrease at an increase in temperature. This has the effect that the amplitude of the deflection current and hence the deflection of the cathode-ray beam decrease.

The invention has for its object to provide an amplifier which obviates this disadvantage and which is characterized in that in order to obtain a current through the output impedance substantially independent of temperature the negative feed-back voltage is taken from a potentiometer which is connected in parallel with the output impedance, at least one branch of the potentiometer comprising a temperature-dependent element which is exposed to the same or substantially the same temperature variations as the output impedance.

In order that the invention may be readily carried into effect, it will now be described in detail with reference to the accompanying drawing.

The drawing shows an amplifier for tooth current for a deflection coil.

To the input terminals 1 is supplied a sawtooth voltage, which serves as a control-voltage for the amplifying tube 2. The anode circuit of the tube 2 comprises a transformer 3, the secondary winding of which is connected to a deflection coil 4, of which one end is connected to ground.

In parallel with the deflection coil is connected a potentiometer comprising branches 5 and 6. From the branch 6 is derived a voltage which is supplied in series with the input voltage to the control-grid of the tube 2.

As has been explained, the resistance of the coil 4 in creases at an increase in temperature.

At least one of the branches 5 and 6 of the potentiometer is constructed in the form of a temperature-dependent resistor and arranged in a manner such that this resistor is exposed to substantially the same temperature variations as the coil 4.

If the element 5 is constructed in the form of a temperature-dependent resistor, this resistor must have a positive temperature coefficient. However, if the element 6 is constructed in the form of a temperature-dependent resistor, this element must have a negative temperature producing a sawnited States Patent Ofltice 2,768,325 Patented Oct. 23, 1956 coeflicient. The coil 4 and. the resistor 5 may be given positive temperature coeflicients by constructing them of metal wire, and the resistor 6 may be given a negative temperature coeflicient by constructing it of carbon.

In the amplifiers according to the invention a satisfactory compensation of the efiects of temperature is obtained, since the temperature-dependent element is housed in a potentiometer, through which only low current need flow, so that this element is substantially not heated additionally.

It will be obvious that in amplifiers in which the output impedance has a negative temperature coeflicient the polarity of the temperature coeflicient of the elements 5 or 6 must be exchanged.

While we have thus described our invention with specific examples and embodiments thereof, other modifications will be readily apparent to those skilled in the art without departing from the spirit and the scope of the invention as defined in the appended claims.

What is claimed is:

1. In a television receiver, an amplifier for supplying a stabilized signal current to a deflection coil, comprising an electron discharge device having an input circuit and an output circuit, means for applying an input signal voltage to said input circuit, means connecting said deflection coil to receive signal current from said output circuit, said deflection coil having a value of impedance which varies with a change in temperature which occurs during the warm-up period of said receiver after being turned on, a potentiometer having a tap thereon connected in parallel with said deflection coil, at least one branch of said potentiometer having a temperature-dependent element, the resistance of which varies with temperature substantially in proportion to said change of impedance of said deflection coil and exposed to substantially the same temperature variations as said deflection coil, and means connecting said tap to said input circuit to apply a negative feedback voltage to said electron discharge device thereby to obtain a substantially temperature-independent current through said deflection coil.

2. An amplifier, as set forth in claim 1, wherein said deflection coil impedance has a positive temperature coeflicient, wherein said temperature-dependent element of perature coeflicient element.

3. amplifier, as set forth in claim 1, Where said deflection C011 impedance has a positive temperature co- 4. An amplifier, as set forth in claim 1, wherein said deflection coil impedance has a negative temperature cceflicient, wherein said temperature-dependent element of one of said branches is a positive temperature coefiicient element, and wherein said negative feedback voltage is obtained from across the branch having said positive temperature coeflicient element.

5. An amplifier, as set forth in claim 1, wherein said deflection coil impedance has a negative temperature coefiicient, wherein said potentiometer includes a first impedance branch and a second impedance branch, said second branch consisting of a negative temperature coefficient element exposed to substantially the same temperature variations as said deflection coil impedance, and wherein said negative feedback voltage is obtained from across said first impedance branch.

References Cited in the file of this patent UNITED STATES PATENTS Rieber Dec. 31, 1935 4 Peterson Dec. 28, 1937 Weathers May 5, 1942 Cowley et a1. Nov. 19, 1946 Nagel Jan. 21, 1947 Bellman Sept. 2, 1947 Wissell June 10, 1952 Roche Sept. 23, 1952 

